Auto-injector

ABSTRACT

An auto-injector for administering a dose of a liquid medicament (M) comprises of a substantially cylindrical housing arranged to contain a pre-filled syringe with an injection needle, a plunger and a stopper for sealing a syringe barrel and a drive means releasably coupled to the plunger for advancing the syringe in the proximal direction (P) for needle insertion into an injection site and for displacing the dose of medicament (M) into the injection site. The drive means is arranged to be decoupled from the plunger for advancing a needle shroud to a safe position (PS) to surround the injection needle after the injection. According to the invention, the drive means bears against a thrust collar arranged to be releasably coupled to the plunger through a ramped engagement of a first tongue and a first recess so as to rotate the thrust collar on translation in proximal direction (P). At least one longitudinal gap (G 1,  G 2 ) is provided for guiding at a first and/or second protrusion of the thrust collar to prevent a rotation of the thrust collar. A circumferential gap (G 3 ) is arranged to allow the thrust collar to rotate out of engagement to the plunger on removal of the auto-injector from the injection site.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a reissue application of U.S. Pat. No.9,272,098, which is a U.S. National Phase Application pursuant to 35U.S.C. §371 of International Application No. PCT/EP2011/073505 filedDec. 21, 2011, which claims priority to European Patent Application No.10196070.6 filed Dec. 21, 2010 and U.S. Provisional Patent ApplicationNo. 61/432,250 filed Jan. 13, 2011. The entire disclosure contents ofthese applications are herewith incorporated by reference into thepresent application.

TECHNICAL FIELD

The invention relates to an auto-injector for administering a dose of aliquid medicament.

BACKGROUND

Administering an injection is a process which presents a number of risksand challenges for users and healthcare professionals, both mental andphysical.

Injection devices (i.e. devices capable of delivering medicaments from amedication container) typically fall into two categories—manual devicesand auto-injectors.

In a manual device—the user must provide the mechanical energy to drivethe fluid through the needle. This is typically done by some form ofbutton/plunger that has to be continuously pressed by the user duringthe injection. There are numerous disadvantages to the user from thisapproach. If the user stops pressing the button/plunger then theinjection will also stop. This means that the user can deliver anunderdose if the device is not used properly (i.e. the plunger is notfully pressed to its end position). Injection forces may be too high forthe user, in particular if the patient is elderly or has dexterityproblems.

The extension of the button/plunger may be too great. Thus it can beinconvenient for the user to reach a fully extended button. Thecombination of injection force and button extension can causetrembling/shaking of the hand which in turn increases discomfort as theinserted needle moves.

Auto-injector devices aim to make self-administration of injectedtherapies easier for patients. Current therapies delivered by means ofself-administered injections include drugs for diabetes (both insulinand newer GLP-1 class drugs), migraine, hormone therapies,anticoagulants etc.

Auto-injectors are devices which completely or partially replaceactivities involved in parenteral drug delivery from standard syringes.These activities may include removal of a protective syringe cap,insertion of a needle into a patient's skin, injection of themedicament, removal of the needle, shielding of the needle andpreventing reuse of the device. This overcomes many of the disadvantagesof manual devices. Injection forces/button extension, hand-shaking andthe likelihood of delivering an incomplete dose are reduced. Triggeringmay be performed by numerous means, for example a trigger button or theaction of the needle reaching its injection depth. In some devices theenergy to deliver the fluid is provided by a spring.

US 2002/0095120 A1 discloses an automatic injection device whichautomatically injects a pre-measured quantity of fluid medicine when atension spring is released. The tension spring moves an ampoule and theinjection needle from a storage position to a deployed position when itis released. The content of the ampoule is thereafter expelled by thetension spring forcing a piston forward inside the ampoule. After thefluid medicine has been injected, torsion stored in the tension springis released and the injection needle is automatically retracted back toits original storage position.

SUMMARY

It is an object of the present invention to provide an improvedauto-injector.

The object is achieved by an auto-injector according to claim 1.

Preferred embodiments of the invention are given in the dependentclaims.

In the context of this specification, the terms distal and proximal aredefined from the point of view of a person receiving an injection.Consequently, a proximal direction refers to a direction pointingtowards the body of a patient receiving the injection and a proximal enddefines an end of an element that is directed towards the body of thepatient. Respectively, the distal end of an element or the distaldirection is directed away from the body of the patient receiving theinjection and opposite to the proximal end or proximal direction.

An auto-injector for administering a dose of a liquid medicamentcomprises

-   -   a substantially cylindrical housing arranged to contain a        pre-filled syringe with an injection needle, a plunger and a        stopper for sealing a syringe barrel and    -   a drive means releasably coupled to the plunger for advancing        the syringe in the proximal direction for needle insertion into        an injection site and for displacing the dose of medicament into        the injection site. The drive means is arranged to be decoupled        from the plunger for advancing a needle shroud to a safe        position to surround the injection needle after the injection.

According to the invention the drive means bears against a thrust collararranged to be releasably coupled to the plunger through a rampedengagement so as to rotate the thrust collar on translation in theproximal direction, wherein guiding means are provided for guiding thethrust collar during at least a part of its axial translation wheninserting the needle and displacing the medicament to prevent a rotationof the thrust collar, wherein the thrust collar is arranged to rotateout of engagement to the plunger on removal of the auto-injector fromthe injection site.

The ramped engagement between the thrust collar and the plunger maycomprise a first tongue and a first recess engageable in a manner torotate the thrust collar on translation in the proximal direction. Atleast one longitudinal gap may be provided as the guiding means forguiding a first or second protrusion of the thrust collar to prevent arotation of the thrust collar. A circumferential gap may be arranged toallow the thrust collar to rotate out of engagement to the plunger onremoval of the auto-injector from the injection site.

A crucial step in delivering medicaments with auto-injectors is thedecoupling of the plunger from the drive means at the appropriate pointin time. If the plunger is decoupled early, the dose of the medicamentmight not be completely expelled. Consequently, the medicament ispartially wasted during the injection. However, such an early releasemight be necessary to ensure that the plunger is decoupled at the end ofan injection stroke, so that in particular functions that ensure needlesafety are reliably carried out. The injection mechanism of theauto-injector is designed in a manner that allows for a completeemptying of the syringe barrel containing the dose of the medicamentbefore the plunger is decoupled from the drive means withoutcompromising needle safety. According to the invention, the plunger isreleasably coupled to a thrust collar. The coupling between the thrustcollar and plunger is released upon rotation. The rotation between thethrust collar relative to the plunger may be caused by the first tongueengaging the first recess. No radial space is taken up for the releasemechanism of the plunger and the thrust collar, so that theauto-injector may be designed in a particularly compact manner.Furthermore, the auto-injector comprises only a few parts and may thusbe cost-efficiently produced.

At least one longitudinal gap may be provided that accommodates a firstor second protrusion formed to the thrust collar. The first or secondprotrusion travels along the at least one gap when the thrust collarcoupled to the plunger is driven proximally by the drive means, wherebya rotation of the thrust collar is prevented until the stopper, which ispushed proximally by the plunger to expel the dose of the medicament,reaches the proximal end of the syringe barrel and the first and/orsecond protrusion reaches the circumferential gap. The circumferentialgap allows the thrust collar to rotate, whereby the thrust collar isdecoupled from the plunger when the dose of medication has beencompletely injected and the auto-injector is removed from the injectionsite.

According to one possible embodiment of the invention, the thrust collaris releasably mounted to a coupling shroud rotationally fixed to thehousing and firmly attached to the plunger. The coupling between theplunger and the thrust collar is released by disconnecting the thrustcollar from the coupling shroud by rotating the thrust collar relativeto coupling shroud.

According to another possible embodiment of the invention, the needleshroud is biased in the proximal direction towards an initial advancedposition and slidable from the advanced position in a distal directionto a retracted position. In particular, the needle shroud may be slid tothe retracted position by placing the auto-injector onto the skin of thepatient receiving the injection and pressing the needle shroud againstthe skin of the patient. The needle shroud in the retracted positionactivates the delivery mechanism of the auto-injector delivering themedicament to the patient by releasing the drive means. The needleshroud is slidable from the retracted position in the proximal directionbeyond the advanced position to the safe position, wherein the needleshroud surrounds the injection needle of the pre-filled syringe andprotrudes beyond the needle tip in the proximal direction sufficient toprevent accidental needle stick injuries after the injection has beencarried out.

Preferably, the needle shroud is arranged to prevent rotation of thethrust collar and thus release of the connection between the couplingshroud and the thrust collar until the dose of the medicament has beencompletely expelled and the auto-injector is withdrawn from theinjection site. The auto-injector provides a reliable mechanism thatcovers the injection needle to avoid accidental needle stick injuriesafter the injection without wasting any medicament initially containedin the pre-filled syringe.

In one possible embodiment of the invention, the needle shroudincorporates a u-shaped indentation for receiving the second protrusionof the thrust collar in the retracted position. The second protrusion isretained in the u-shaped indentation to rotationally affix the thrustcollar after full delivery of the medicament and until the needle shroudleaves the retracted position, which may in particular be achieved byremoving the auto-injector from the injection site after the dose of themedicament has been injected. Thus, the needle shroud with the u-shapedindentation prevents the release of the connection between the thrustcollar and the coupling shroud until the stopper has bottomed out andthe injection is completed. The needle shroud is arranged to open thecircumferential gap on translation into the advanced position forallowing the thrust collar to rotate out of engagement to the plunger.The auto-injector is suitable to be used for administering relativeexpensive medicaments as it is designed to completely empty the syringebarrel containing the dose of the medicament.

According to another possible embodiment of the invention, the needleshroud is releasably mounted to the housing by a clip preventing travelin the proximal direction beyond the advanced position. The thrustcollar is disconnected from the coupling shroud at the end of theinjection stroke delivering the medication. Upon the release, the thrustcollar is driven proximally by the drive means to engage and deflect theclip to release the needle shroud. The needle shroud is then allowed tobe moved in the proximal direction to the safe position, wherein theinjection needle is covered to prevent accidental needle stick injuries.

According to another embodiment of the invention, a syringe retainer isarranged for mounting the syringe within the housing, wherein aretaining element is attached to the syringe retainer. The retainingelement releasably couples the plunger to the syringe retainer. A forceexerted upon the plunger by the drive means is thus directed via theretaining element to the syringe retainer, so that the syringe retainercarrying the pre-filled syringe may be moved in the proximal directionto insert the injection needle into the skin of the patient, whereby adisplacement of the plunger relative to the syringe barrel containingthe dose of the medicament is avoided. This prevents a prematureexpelling of the medicament before the injection needle penetrates theskin of the patient. Thus, unpleasant wet injections are avoided.

The retaining element may comprise at least one first catch that latchesto a notch formed into the plunger to releasably couple the plunger tothe syringe retainer. The first catch is released by a radial deflectionand thus operates independently of the angular orientation of thecoupling shroud and the thrust collar.

Preferably, the first catch is arranged to abut against an inner sleeveof the housing to prevent the decoupling of the plunger and the syringeretainer. An aperture is formed into the inner sleeve that allows for aradial outward deflection of the first catch to decouple the syringeretainer from the plunger. The aperture is located in a position thatensures that the decoupling takes place when the syringe retainer is ina proximal position and the injection needle protrudes from the proximalend of the auto-injection by a length that corresponds to a desiredinjection depth. The aperture is formed into the inner sleeve and isshielded by an outer casing of the housing. This prevents a user tryingto re-use the auto-injector after an injection has been completed, bytampering with the first catch retained in the aperture. Theauto-injector is designed as a single use device to minimize the risk ofinfections that are transmitted by needle stick injuries with usedinjection needles.

According to another possible embodiment of the invention, the couplingshroud comprises a flat first lateral wall that abuts against acorresponding flat second lateral wall of the inner sleeve to prevent arotation of the coupling shroud relative to the housing. The interactionof the first and second lateral walls comprises a simple and effectivemeans to ensure that the coupling shroud is rotationally affixed to thehousing. This in turn ensures that the thrust collar may be reliablydisconnected by a rotation about a relative small angle with respect tothe coupling shroud.

According to yet another possible embodiment of the invention, a biasingmeans biases the needle shroud in the proximal direction. The biasingmeans and the drive means are fitted into each other to optimally useavailable space within the housing. This allows for a particular compactdesign of the auto-injector.

The biasing means is arranged as a compression spring having a diameterthat differs from the diameter of the drive means in a manner thatallows the drive means and the biasing means to expand independentlyfrom each other without interfering. The two nested compression springsprovide a simple arrangement to efficiently use the space availablewithin the housing of the auto-injectors and are inexpensive to produce.

According to yet another possible embodiment of the invention, the drivemeans is arranged as a single compression spring. The mechanism of theauto-injector is arranged in a manner that a plurality of functions isexecuted by the single drive means. The injection needle is insertedinto the skin of the patient, the plunger is translated to expel themedicament and the needle shroud is moved proximally to provide needlesafety after the injection is completed by the action of the springmeans. Conventional auto-injectors usually comprise a plurality ofspring means to accomplish these tasks. The auto-injector according tothe invention comprises only few parts and is particularly inexpensiveto mass-produce. Consequently, the auto-injector is particularly suitedas a single-use device that may be disposed after an injection has beencarried out.

In another possible embodiment of the invention, a rotating collar isarranged within the housing and axially fixed to the housing of theauto-injector. The rotating collar engages the needle shroud in a mannerthat forces the rotating collar to rotate within the housing when theneedle shroud is axially displaced from the advanced position into thesafe position. The rotating collar creates friction to slow down theproximal movement of the needle shroud that rests on the skin of thepatient during the injection. The rotating collar acts as a dampeningelement that alleviates the pressure exerted upon the skin of thepatient by the needle shroud. Thus, the risk of injuries is reduced and,in particular, bruises may be avoided. Furthermore, the modulus ofresilience of the single drive means driving the needle shroud may bechosen to be sufficiently large without having to worry about potentialinjury risks. Thus, the modulus of resilience of the drive means isadapted to reliably provide an energy supply for executing a pluralityof actions comprising, among others, the advancing and releasing of theneedle shroud, the displacement of the stopper to expel the medicamentand the decoupling of the plunger and the coupling shroud.

Preferably, the rotating collar comprises a pin that engages a trackformed into the needle shroud. The track comprises a straight firstsection for guiding the pin between the retracted position and theadvanced position and a second section oriented at an angle with respectto the first section for guiding the pin between the advanced positionand the safe position. The pin travels along the track when the needleshroud is axially displaced. When the pin travels along the angledsecond section of the track, the rotating collar is forced to rotatearound the needle shroud. This dampens the proximal movement of theneedle shroud and thus reduces the pressure exerted upon the skin of thepatient by generating friction.

The auto-injector may preferably be used for subcutaneous orintra-muscular injection, particularly for delivering one of ananalgetic, an anticoagulant, insulin, an insulin derivate, heparin,Lovenox, a vaccine, a growth hormone, a peptide hormone, a protein,antibodies and complex carbohydrates.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus, are not limitiveof the present invention, and wherein:

FIGS. 1A and 1B show two different sectional views of the auto-injectorbefore an injection;

FIG. 2 shows in a perspective view a thrust collar connected to acoupling shroud by a thread connection;

FIG. 3 shows an interior mechanism of the auto-injector in a perspectiveview before an injection;

FIG. 4 shows details of the auto-injector that illustrate the release ofa drive means in a perspective view;

FIG. 5 shows the interior mechanism of the auto-injector in aperspective view after an injection stroke;

FIG. 6 shows the interior mechanism of the auto-injector in aperspective view, wherein the decoupling of the thrust collar and thecoupling shroud is illustrated;

FIG. 7 shows details of the auto-injector that illustrate the release ofa needle shroud;

FIG. 8 shows details of the auto-injector that illustrate the locking ofthe needle shroud in a safe position;

Corresponding parts are marked with the same reference symbols in allfigures.

DETAILED DESCRIPTION

FIGS. 1A and 1B show two sectional views of an essentially cylindricalauto-injector 1, wherein the sectional planes shown are orientedperpendicularly with respect to each other. The auto-injector 1comprises a housing 2, a proximal needle shroud 3, a syringe retainer 4adapted to mount a pre-filled syringe 5 within the housing 2, a couplingshroud 6 slidably arranged within the housing 2 and a thrust collar 7releasably connected to the coupling shroud 6 by a connection that isreleased by rotating the thrust collar 7 relative to the coupling shroud6.

The releasable connection between the thrust collar 7 and the couplingshroud 6 is released by a rotation about a relative small angle aroundthe axis of the substantially cylindrical auto-injector 1, like, forexample, a quarter twist. The thrust collar 7 and the coupling shroud 6may be connected by a bayonet kind of coupling or, alternatively, athread connection with a corresponding lead that allows for a release bya relative small twist.

A drive means 8 is arranged between the distal end of the housing 2 andthe thrust collar 7. The drive means 8 biases the thrust collar 7 in aproximal direction P towards the skin of a patient receiving aninjection. The thrust collar 7 carries a threaded connection to thecoupling shroud 6 with a steep pitch angle, and the coupling shroud 6 isrestrained against rotation relative to the housing 2, so that thethrust collar 7 is additionally biased to rotate around the axis of theauto-injector 1.

According to one possible embodiment of the invention, the drive means 8is arranged as a single, conventional compression spring.

The coupling shroud 6 is firmly attached to a plunger 9 arranged to pushon a stopper 10 fluid-tightly sealing a distal end of a syringe barrel11 containing a dose of a medicament M. A plunger collar 9.2 of theplunger 9 protrudes into a locking recess 6.1 formed into the distal endof the coupling shroud 6 to attach the plunger 9 to the coupling shroud6.

An inner cavity of the syringe barrel 11 is in fluid communication withan injection needle 12, so that the dose of the medicament M may beexpelled through the injection needle 12 by displacing the stopper 10 inthe proximal direction P.

The needle shroud 3 is designed to be pushed against the skin of thepatient during the injection. Edges of the needle shroud 3 may thus besmoothed to avoid injuries. The needle shroud 3 is slidably arrangedwith the housing 2 of the auto-injector 1, so that the needle shroud 3may be pushed from an advanced position PA shown in FIGS. 1A and 1B in adistal direction D. A biasing means 13 bears against the needle shroud 3and the distal end of the housing 2 to bias the needle shroud 3 towardsthe advanced position PA.

The biasing means 13 and the drive means 8 are fitted into each other tooptimally use available space within the housing 2.

In a possible embodiment of the invention, the biasing means 13 isarranged as a compression spring having a diameter that differs from thediameter of the compression spring of the drive means 8 in a manner thatallows the drive means 8 and the biasing means 13 to expandindependently from each other without interfering.

A retaining element 14 is attached to a distal end of the syringeretainer 4 that releasably couples the plunger 9 to the syringe retainer4, so that the syringe retainer 4 may jointly move with the plunger 9 inthe proximal direction P to expose the injection needle 12. Theretaining element 14 comprises at least one and preferably two or morefirst catches 14.1 arranged equi-spaced around retaining element 14,wherein each first catch 14.1 latches to a respective notch 9.1 formedinto the plunger 9. The first catch 14.1 abuts against an inner sleeve2.2 of the housing 2 in the radial outward direction, so that adeflection of the first catch 14.1 and hence a decoupling of the plunger9 and the syringe retainer 4 is prevented.

The plunger 9 is coupled to the retaining element 14 and the syringeretainer 4 until the syringe retainer 4 mounting the pre-filled syringe5 is moved proximally to expose the injection needle 12. A longitudinalaperture 2.3 is formed into the inner sleeve 2.2 of the housing 2 thatallows for a radial outward deflection of the first catch 14.1 when thesyringe retainer 4 is in a proximal position and the injection needle 12is exposed. The plunger 9 is released from the retaining element 14 inthe proximal position and may move proximally to displace the stopper10, whereby the dose of medication M is expelled through the injectionneedle 12.

A ring-shaped rotating collar 15 is circumferentially arranged around atubular proximal section of the needle shroud 3. A pin 15.1 is formed toan inner surface of the rotating collar 15 that engages a track 3.1formed into an outer surface of the needle shroud 3. The track 3.1comprises a straight first section 3.1.1 and a helical second section3.1.2 that can best be seen in FIG. 5. The first section 3.1.1 of thetrack 3.1 extends essentially parallel to the axis of the auto-injector1, whereas the second section 3.1.2 of the track 3.1 is angled withrespect to the first section 3.1.1. As the needle shroud 3 is axiallydisplaced with respect to the housing 2, the pin 15.1 travels along thetrack 3.1, so that the rotating collar 15 is forced to rotate around tothe needle shroud 3. The friction generated by the rotation slows downthe proximal movement of the needle shroud 3 and reduces pressureexerted upon the skin surface of the patient by the needle shroud 3.

FIG. 2 shows the coupling shroud 6 with the thrust collar 7 connectedthereto in a perspective view. The connection between the thrust collar7 and the coupling shroud 6 is releasable upon rotation. A helical firstrecess 6.2 is formed into an outer surface of the coupling shroud 6. Afirst tongue 7.1 that is correspondingly shaped to the first recess 6.2is formed to an inner surface of the thrust collar 7. The first tongue7.1 engages the first recess 6.2 to releaseably connect the couplingshroud 6 and the thrust collar 7 in a thread type connection.

The coupling shroud 6 is slidably arranged within the housing 2 andcomprises a flat first lateral wall 6.3 that abuts a corresponding flatsecond lateral wall 2.4 of the inner sleeve 2.2 to prevent a rotation ofthe coupling shroud 6 relative to the housing 2.

The essentially ring-shaped thrust collar 7 comprises an outer surfacewith a plurality of first and second protrusions 7.2, 7.3 formedthereto. The first and second protrusions 7.2, 7.3 are circumferentiallydisplaced from each other and protrude radially outwards. The firstprotrusions 7.2 have a quadrangular shape, whereas the second protrusion7.3 comprises a triangular shape.

FIG. 3 shows the auto-injector 1 in a perspective view before aninjection is performed. For illustrative purposes, the outer shell 2.1of the housing 2 is not shown. FIG. 3 illustrates an interior mechanismof the auto-injector 1 that is hidden from view by the outer case 2.2during normal use. The needle shroud 3 is positioned in the advancedposition PA.

The quadrangular first protrusion 7.2 comprises a first ramp 7.2.1 thatabuts against a corresponding second ramp 2.5 formed to the housing 2.Furthermore, the first protrusion 7.2 abuts against the needle shroud 3in a circumferential direction. Before the injection, the biased thrustcollar 7 is retained in a first position I by the first protrusion 7.2abutting against the needle shroud 3 and the second ramp 2.5 of thehousing 2.

The injection is initiated by pressing the needle shroud 3 against theskin of the patient receiving the injection, whereby the needle shield 3is displaced from the advanced position PA in the distal direction D toa retracted position PR. As shown in detail in FIG. 4, the distalmovement of the needle shroud 3 to the retracted position PR makes wayfor a circumferential displacement of first protrusion 7.2. The thrustcollar 7 rotates around the axis of the auto-injector 1 by a smallangle, insufficient to release thrust collar 7 from coupling shroud 6.The first protrusion 7.2 is guided by the first and second ramps 7.2.1,2.5 into a longitudinal first gap G1 between the needle shroud 3 and thehousing 2. The thrust collar 7 blocking the drive means 8 is nowreleased. The fully compressed drive means 8 drives the thrust collar 7and the coupling shroud 6 connected thereto in the proximal direction P,whereby the first protrusion 7.2 travels along the first gap G1 in theproximal direction P. At the same time the second protrusion 7.3 travelsproximally along a longitudinal second gap G2 that is arranged betweenthe housing 2 and the needle shroud 3 in a similar manner as the firstgap G1. As the first Gap G1 is arranged to limit a circumferentialdisplacement of the first protrusion 7.2, a further rotation of thethrust collar 7 is prevented until an injection stroke delivering thedose medication M is completed.

The thrust collar 7 is connected to the coupling shroud 6 that isattached to the plunger 9. The plunger 9 in turn is coupled to syringeretainer 4 via the retaining element 14. Thus, the coupling shroud 6driven by the drive means 8 first translates the syringe retainer 4holding the pre-filled syringe 5 in the proximal direction P until thesyringe retainer 4 bears against a bearing surface 2.6 formed to thehousing 2 as best seen in FIG. 1A. The bearing surface 2.6 defines aninjection depth of the injection needle. The injection needle 12 nowprotrudes from the needle shroud 3 in the proximal direction P andpenetrates the skin surface of the patient at the desired injectiondepth.

The deflectable first catches 14.1 that couple the plunger 9 to thesyringe retainer 4 are now located adjacent to the longitudinalapertures 2.3 formed into the inner sleeve 2.2 of the housing 2. Thefirst catches 14.1 deflect in the radial outward direction due to theirramped engagement with the notches 9.1 and disengage from the notches9.1 to decouple the plunger 9 from the syringe retainer 4.

The drive means 8 further relaxes and drives the coupling shroud 6, thethrust collar 7 and the plunger 9 in the proximal direction P. Theplunger 9 pushes the stopper 10 proximally to expel the dose ofmedication M contained in the syringe barrel 11 through the injectionneedle 12.

When the stopper 10 reaches a proximal end of the syringe barrel 11, theinjection stroke is completed and the dose of medication M is completelyexpelled. At the same time, the thrust collar 7 reaches a proximalsecond position II shown in FIG. 5.

FIG. 5 shows the auto-injector 1 in a perspective view after theinjection stroke is completed. Similar to FIGS. 3 and 4, the outer shell2.1 is not shown to illustrate the interior mechanism of auto-injector1.

The needle shroud 3 is still pressed against the injection site toretain the needle shroud 3 in the retracted position PR. At the sametime, the thrust collar 7 is located in the second position II. Thetriangular second protrusion 7.3 of the thrust collar 7 is retained in au-shaped indentation 3.2 formed to the needle shroud 3. The u-shapedindentation 3.2 constitutes a proximal end of the second gap G2 andcomprises a circumferential width that corresponds to the secondprotrusion 7.3. The u-shaped indentation 3.2 abuts against the secondprotrusion 7.3 in the circumferential direction, so that a rotation ofthe thrust collar 7 and thus a decoupling of the thrust collar 7 and thecoupling shroud 6 are prevented until the needle shield 3 leaves theretracted position PR.

The auto-injector 1 is removed from the injection site. The biasingmeans 13 relaxes to return the needle shroud 3 to the advanced positionPA. As a consequence, the needle shroud 3 moves proximally with respectto the housing 2 and the thrust collar 7 connected to the couplingshroud 6.

FIG. 6 shows the interior mechanism of the auto-injector 1 in aperspective view after the auto-injector 1 has been removed from theinjection site. The proximal movement of the needle shroud 3 opens acircumferential gap G3 between the housing 2 and the needle shroud 3.The triangular second protrusion 7.3 travels through the circumferentialgap G3 in the circumferential direction, whereby the thrust collar 7slightly rotates around the axis of the auto-injector 1 due to theramped engagement of the first tongue 7.1 with the first recess 6.2. Thedrive means 8 bears against the thrust collar 7 and pushes a third ramp7.3.1 on the second protrusion 7.3 against a corresponding fourth ramp3.3 on the needle shroud 3 when the thrust collar 7 is located in anintermediate third position III. The thrust collar 7 tries to rotate dueto its threaded connection with the coupling shroud 6.1 relative to thehousing 2 and relative to the coupling shroud 6. If a bayonet connectionwas used instead of the thread the third and fourth ramp 7.3.1, 3.3would cause the thrust collar 7 to further rotate. This final rotationof the thrust collar 7 suffices to decouple the coupling shroud 6 andthe thrust collar 7. The decoupled thrust collar 7 is then drivenfurther in the proximal direction P by the drive means 8 until an innersurface of the thrust collar 7 engages a fifth ramp 2.7 of a clip 2.8connecting the housing 2 with the needle shroud 3 that is shown in moredetail in FIG. 7.

FIG. 7 shows the release of the substantially t-shaped clip 2.8 thatmounts the needle shroud 3 to the housing 2. The t-shaped clip 2.8 isretained in a second recess 3.4 formed in the needle shroud 3. Thesecond recess 3.4 comprises axial dimensions that allow for a slidingmovement of the needle shroud 3 relative to the housing 2 between theadvanced position PA and the retracted position PR while the clip 2.8 isretained in the second recess 3.4.

The clip 2.8 is deflectable in the radial inward direction to releasethe needle shroud 3. As shown in FIG. 7, the thrust collar 7 slides overthe fifth ramp 2.7 to bend the clip 2.8 radially inwards after thethrust collar 7 and coupling shroud 6 have been decoupled. The t-shapedclip 2.8 is deflected inwards and disengages from the second recess 3.4,so that the needle shroud 3 may be proximally advanced towards a safeposition PS. The drive means 8 further relaxes and pushes the decoupledthrust collar 7 further in the proximal direction P. The thrust collar 7bears against the needle shroud 3 to advance the needle shroud 3 towardsthe safe position PS shown in more detail in FIG. 8.

When the needle shield 3 moves proximally from the advanced position PAto the safe position PS, the pin 15.1 of the rotating collar 15 travelsalong the second section 3.1.2 of the track 3.1 formed into the needleshroud 3. As the second section 3.1.2 is oriented at an angle withrespect to the axis of the auto-injector, the translatory movement ofthe needle shroud 3 causes the rotating collar 15 to rotate around theaxis, whereby friction is generated. The generated friction slows downand damps the proximal movement of the needle shroud 3.

FIG. 8 shows a perspective view of the interior mechanism of theauto-injector 1, wherein the needle shroud 3 is locked in the safeposition PS. In the safe position PS, the needle shroud 3 protrudesproximally from the housing 2 of the auto-injector 1 and permanentlysurrounds and protrudes proximally beyond the tip of the injectionneedle 12 after an injection to prevent accidental needle stickinjuries.

As the thrust collar 7 and the needle shroud 3 have travelled proximallybeyond the clip 2.8, the clip 2.8 deflects outwards to return to itsprior position. The needle shroud 3 abuts against the t-shaped clip 2.8in the distal direction D, so that a distal movement of the needleshroud 3 in the safe position PS relative to the housing 2 is prevented.Thus, the needle shroud 3 is permanently locked in the safe position PSand a re-exposure of the injection needle 12 is prevented. The thrustcollar 7 travelled over the fifth ramp 2.7 and is located in a maximumproximal fourth position IV, wherein the thrust collar 7 abuts theneedle shroud 3.

The invention claimed is:
 1. Auto-injector for administering a dose of aliquid medicament (M), comprising: a substantially cylindrical housingarranged to contain a pre-filled syringe with an injection needle, aplunger and a stopper for sealing a syringe barrel and a driverreleasably coupled to the plunger for advancing the syringe in theproximal direction (P) for needle insertion into an injection site andfor displacing the dose of medicament (M) into the injection site,wherein the driver is arranged to be decoupled from the plunger foradvancing a needle shroud to a safe position (PS) to surround theinjection needle after the injection, wherein the driver bears against athrust collar arranged to be releasably coupled to the plunger through aramped engagement so as to rotate the thrust collar on translation inproximal direction (P), wherein guiding mechanism are provided forguiding the thrust collar during at least a part of its axialtranslation when inserting the needle and displacing the medicament (M)to prevent a rotation of the thrust collar, wherein the thrust collar isarranged to rotate out of engagement to the plunger on removal of theauto-injector from the injection site.
 2. Auto-injector according toclaim 1, wherein the ramped engagement between the thrust collar and theplunger comprises a first tongue and a first recess, wherein the guidingmechanism comprises at least one longitudinal gap (GI, G2) for guiding afirst or second protrusion of the thrust collar, wherein acircumferential gap (G3) is arranged to allow the thrust collar torotate out of engagement to the plunger on removal of the auto-injectorfrom the injection site.
 3. Auto-injector according to claim 1, whereinthe thrust collar is releasably mounted to a coupling shroudrotationally fixed to the housing and firmly attached to the plunger,wherein the connection between the thrust collar and the coupling shroudis releasable by a relative rotation between the thrust collar and thecoupling shroud.
 4. Auto-injector according to claim 1, wherein theneedle shroud is biased in a proximal direction (P) towards an advancedposition (PA) and slidable from the advanced position (PA) in a distaldirection (D) to a retracted position (PR) and from the retractedposition (PR) in the proximal direction (P) beyond the advanced position(PA) to the safe position (PS), wherein sliding the needle shroud fromthe advanced position (PA) to the retracted position (PR) releases thedriver.
 5. Auto-injector according to claim 4, wherein at the needleshroud in the refracted position (PR) is arranged to prevent rotation ofthe thrust collar, thus preventing the release of the connection betweenthe thrust collar and the coupling shroud.
 6. Auto-injector according toclaim 5, wherein the needle shroud comprises au-shaped indentation forreceiving the second protrusion of the thrust collar to prevent therelease of the connection between the thrust collar and the couplingshroud in the retracted position (PR), wherein the needle shroud isarranged to open the circumferential gap (G3) on translation into theadvanced position (PA) for allowing the thrust collar to rotate out ofengagement to the plunger.
 7. Auto-injector according to claim 1,wherein at the needle shroud is releasably mounted to the housing by aclip preventing travel in proximal direction (P) beyond the advancedposition (PA), wherein the thrust collar is arranged to radially deflectthe clip for releasing the needle shroud allowing it to be moved in theproximal direction (P) to the safe position (PS).
 8. Auto-injectoraccording to claim 1, wherein a syringe retainer is arranged formounting the syringe within the housing, wherein a retaining element isattached to the syringe retainer, wherein the release element releasablycouples the plunger to the syringe retainer.
 9. Auto-injector accordingto claim 8, wherein the retaining element comprises at least one firstcatch that latches to a notch formed into the plunger to releasablycouple the plunger to the syringe retainer.
 10. Auto-injector accordingto claim 8, wherein the first catch is arranged to abut against an innersleeve of the housing to prevent decoupling of the plunger and thesyringe retainer, wherein an aperture is formed into the inner sleeveallowing for a radial outward deflection of the first catch to decouplethe syringe retainer from the plunger when the syringe retainer is in aproximal position.
 11. Auto-injector according to claim 10, wherein thecoupling shroud comprises a flat first lateral wall that abuts against acorresponding flat second lateral wall of the inner sleeve to prevent arotation of the coupling shroud relative to the housing. 12.Auto-injector according to claim 1, wherein a biasing mechanism biasesthe needle shroud in the proximal direction (P), wherein the biasingmechanism and the driver are fit into each other to optimally useavailable space within the housing.
 13. Auto-injector according to claim1, wherein the driver is arranged as a single compression spring. 14.Auto-injector according to claim 13, wherein the single compressionspring is strained only translationally.
 15. Auto-injector according toclaim 1, wherein a rotating collar axially fixed to the housing engagesthe needle shroud in a manner that forces the rotating collar to rotatewithin the housing when the needle shroud is axially displaced from theadvanced position (PA) into the safe position (PS).
 16. Auto-injectoraccording to claim 1, wherein the rotating collar comprises a pin thatengages a track formed into the needle shroud, wherein the trackcomprises a straight first section for guiding the pin between theretracted position (PR) and the advanced position (PA) and a helicalsecond section for guiding the pin between the advanced position (PA)and the safe position (PS).
 17. An auto-injector for administering adose of a liquid medicament, the auto-injector comprising: a housingdefining a cavity configured to receive a syringe; a thrust membercomprising a radial projection, the radial projection configured toengage a ramped surface within the housing when the thrust member is ina first rotational position and to disengage from the ramped surfacewhen the thrust member is moved to a second rotational position; a drivespring disposed within the housing and configured to apply an axialforce to the thrust member such that when the thrust member is in thefirst rotational position, the engagement between the radial projectionand the ramped surface biases the thrust member from the firstrotational position toward the second rotational position; and a needleshroud configured to move from an extended position to a retractedposition, the needle shroud having a surface configured to engage theradial projection to inhibit rotation of the thrust member relative tothe needle shroud when the needle shroud is in the extended positon andthe thrust member is in the first rotational position, and the needleshroud defining an opening arranged to receive the radial projectionwhen the needle shroud is in the retracted positon to allow the thrustmember to rotate from the first rotational position to the secondrotational position, and the opening being arranged to permit the radialprojection to move axially within the opening when the thrust member hasbeen rotated to the second rotational position and is moved axially bythe drive spring.
 18. The auto-injector of claim 17, wherein the rampedsurface is a surface of the housing.
 19. The auto-injector of claim 18,wherein the radial projection of the thrust member has a ramp thatengages the ramped surface within the housing when the thrust member isin the first rotational position.
 20. The auto-injector of claim 19,wherein the radial projection of the thrust member is quadrangular inshape.
 21. The auto-injector of claim 17, wherein the thrust membercomprises a plunger configured to contact a stopper of the syringe andadvance the stopper within a chamber of the syringe to administer thedose of the liquid medicament when the thrust member is moved axially bythe drive spring and the syringe is disposed within the cavity of thehousing.
 22. The auto-injector of claim 17, wherein the thrust member iscoupled to the syringe when the syringe is disposed in the cavity of thehousing, and the thrust member is configured to advance the syringeaxially within the housing when the thrust member is moved axially bythe drive spring.
 23. The auto-injector of claim 17, wherein the surfaceof the needle shroud that is configured to engage the radial projectionof the thrust member is a longitudinal surface that is configured tocircumferentially engage the radial projection.
 24. The auto-injector ofclaim 17, wherein the opening of the needle shroud includes a firstportion and a second portion, at least part of the second portion beingcircumferentially offset from the first portion.
 25. The auto-injectorof claim 24, wherein the first portion of the opening is defined atleast in part by the surface of the needle shroud that is configured toengage the radial projection of the thrust member such that the radialprojection resides within the first portion of the opening when thethrust member is in the first rotational position.
 26. The auto-injectorof claim 25, wherein the opening of the needle shroud is arranged topermit the radial projection of the thrust member to move axially withinthe second portion of the opening when the thrust member has beenrotated to the second rotational position and is moved axially by thedrive spring.
 27. The auto-injector of claim 17, wherein the needleshroud is configured to move from the retracted position to a safeposition in which the needle shroud extends forward of the housing. 28.The auto-injector of claim 27, wherein a portion of the housing isconfigured to engage the needle shroud to lock the needle shroud in thesafe position.
 29. The auto-injector of claim 28, wherein the portion ofthe housing that is configured to engage the needle shroud is a clipthat extends radially inward from a body of the housing.
 30. Theauto-injector of claim 28, wherein the shroud and the housing areconfigured such that an end of the shroud moves beyond the portion ofthe housing that is configured to engage the needle shroud when theneedle shroud is moved to the safe position thereby allowing the portionof the housing to engage an end surface of the needle shroud.
 31. Theauto-injector of claim 17, further comprising a needle shroud springthat biases the needle shroud toward the extended position.
 32. Theauto-injector of claim 17, wherein the opening of the needle shroud isat least partially defined by an axially extending arm of the needleshroud.
 33. The auto-injector of claim 32, wherein the needle shroudfurther comprises a cylindrical end body from which the axiallyextending arm extends.
 34. The auto-injector of claim 17, furthercomprising the syringe disposed in the cavity of the housing.
 35. Theauto-injector of claim 34, wherein the syringe defines a chambercontaining the liquid medicament and a stopper slidably arranged withinthe chamber.
 36. The auto-injector of claim 35, wherein the syringefurther comprises an injection needle in fluid communication with thechamber.
 37. The auto-injector of claim 36, wherein the needle shroud isconfigured to surround at least a portion of the needle when the needleshroud is in the extended position.
 38. The auto-injector of claim 17,further comprising a syringe retainer defining a chamber configured toreceive the syringe, the cavity of the housing being configured toreceive both the syringe retainer and the syringe disposed in thechamber of the syringe retainer.